1. Field of the Invention
The present invention relates to an organic electroluminescence (EL) display device, in particular, a reliable top emission type organic EL display device in which generation of a dark spot caused by moisture is suppressed, and a method of manufacturing the same.
2. Description of the Related Art
In an organic EL display device, an organic EL layer is sandwiched between a lower electrode (first electrode) and an upper electrode (second electrode), a constant voltage is applied to the upper electrode, and a data signal voltage is applied to the lower electrode so as to control light emission of the organic EL layer, thereby forming an image. Supply of data signal voltage to the lower electrode is carried out via a thin film transistor (TFT).
The light emitting property of an organic EL material used in the organic EL display device is degraded if moisture exists therein, and when an operation is performed for a long period of time, the organic EL material becomes unable to emit light at a place where the light emitting property has been degraded due to the moisture. The place appears as a dark spot of a display region. This dark spot grows with time, and becomes a defect in an image.
In order to prevent the generation or growth of the dark spot, it is necessary to prevent intrusion of moisture into the organic EL display device. Therefore, the organic EL layer formed on a device substrate is sealed to prevent the intrusion of moisture into the organic EL display device from outside. As for a sealing method for this purpose, various techniques have been developed.
JP 2001-57287 A and JP 2001-176655 A each disclose a basic structure for so-called “hollow sealing”. In the structure disclosed in each of JP 2001-57287 A and JP 2001-176655 A, an organic EL layer is formed on a device substrate, and the device substrate is sealed with a sealing substrate in order to protect this organic EL layer. Further, the sealing substrate or the device substrate is provided with a drying agent, thereby removing moisture that has intruded. Besides, a space is formed between the device substrate and the sealing substrate.
The hollow sealing organic EL display device has problems such as the difficulty of adjusting a gap between the device substrate and the sealing substrate, the difficulty of adjusting pressure inside a sealed region, the contamination of an organic EL material due to gas emitted from a sealing agent when sealing with the sealing agent, and low throughput.
JP 8-111286 A and JP 2000-223264 A each disclose a structure for so-called “solid sealing” provided so as to cope with the problems of the above-mentioned hollow sealing. Specifically, JP 8-111286 A and JP 2000-223264 A each disclose a sealing structure provided by covering a device, on which an organic EL layer is formed, with an inorganic protective film or an organic protective film. However, the structure disclosed in each of JP 8-111286 A and JP 2000-223264 A has a problem in that a sealing effect against moisture is not sufficient as compared with a case where sealing is provided using a glass substrate or metal.
Other solid sealing structures include a structure disclosed in JP 2004-139977 A. JP 2004-139977 A discloses the structure in which a photo-curing resin formed on an optically transparent film is applied onto a device substrate, which is provided with an organic EL layer, with the use of a pressure roller heated to 80° C. Subsequently, the photo-curing resin is cured by ultraviolet radiation, and the optically transparent film is peeled off, thereby obtaining an organic EL display device sealed with the photo-curing resin. JP 2004-139977 A further discloses a structure in which an organic EL element is covered with a silicon nitride film as necessary.
JP 2005-79254 A discloses formation of an SiN film having lower Si—H with the use of plasma CVD. In the example disclosed in JP 2005-79254 A, a substrate temperature is 200° C. Moreover, JP 2004-50821 A discloses formation of an SiNxOy film by ion plating.